In an oil and gas well, a sub-surface safety valve is a downhole valve normally maintained in an open position to allow fluid to flow through the valve. The safety valve is closed to prevent blowout of the well, for example, if an excessive pressure drop or flow occurs across the safety valve. One type of sub-surface safety valve uses a spring and choke mechanism to close the valve if the well flow rate exceeds a predetermined level. Another type uses a pre-charged chamber to close the valve if the pressure caused by increased flow falls below a predetermined value.
Yet another type of sub-surface safety valve is remotely controlled and is commonly referred to as a Surface Controlled Sub-surface Safety Valve (SCSSSV). FIG. 1 shows this type of sub-surface safety valve 10 connected to a tubing assembly 15 downhole. The valve 10 has a flap 18 that is normally biased to block an internal bore 11 of the safety valve 10. To open the flap 18, a single control line 20 communicates hydraulic pressure from a well control panel (not shown) at the surface to a control port 12 of the valve 10. The hydraulic pressure pushes a piston 13 and moves an internal sleeve 14 against a spring force 16 in the valve 10. When moved, the sleeve 14 causes the flap 18 to open so that fluid can pass through the internal bore 11 of the valve 10. To close the valve 10 in response to uncontrolled flow and/or pressure drop, the well control panel at the surface removes the hydraulic pressure applied at the port 12, and the spring force 16 moves the internal sleeve 14, causing the flap 18 to close off the bore 11.
The control line 20, which may be ¼-inch diameter tubing, can fail due to various reasons, which may make the valve 10 inoperable. For example, the control line 20 over time may become contaminated or blocked due to debris in the control fluid. Typical debris, contamination, or particles that can develop and become suspended in the control fluid can come from reservoirs, physical wear of system components, chemical degradation, and other sources. Therefore, it is known in the art to use a filtering system with the control line 20 due to the importance of the safety valve 10.
FIG. 2 shows an existing filtering system used for the control line 20 connected to a sub-surface safety valve 10. The filtering system includes a sump 30 and in-line filter 40. The sump 30 can collect debris contained in the control fluid, and the in-line filter 40 can remove debris from the control fluid. Unfortunately, the existing filtering system can offer less than ideal filtering of the control fluid and may not ensure reliable operation of the safety valve 10. For example, the in-line filter 40 has a tendency to become blocked once it eventually becomes saturated with debris, which can make the safety valve 10 inoperable and can require the filter 40 to be replaced. Moreover, any problems with the control line 20 caused by debris or contamination can render the valve 10 inoperable or may require repairs.
Accordingly, what is needed is a system that can improve the collection of debris and filtering of debris in control fluid communicated to a surface controlled sub-surface safety valve and that can increase the reliability of the safety valve's operation. The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.